arXiv subjects

Alexandre P. Costa

Publications and source records attributed to Alexandre P. Costa.

5 recordsLinked to original sources

arXiv2026

Conditional non-Hermitian acceleration of multiphoton atomic transitions

Continuous monitoring can convert a dissipative channel into a resource for accelerating otherwise slow multiphoton transitions. We consider a three-level atom in a $\Lambda$ configuration and condition the evolution on the absence of photon emission through an auxiliary monitored decay channel. The resulting no-jump dynamics is governed by a non-Hermitian Rabi-type Hamiltonian. Using Floquet theory and Brillouin--Wigner projection-operator perturbation method, we derive effective two-state descriptions of odd-multiphoton resonances in the semiclassical and quantum Rabi models. The effective population-transfer rate, defined as the inverse of the time required for the first complete transfer between the atomic states, is maximized at an exceptional point, where its enhancement factor approaches $\pi/2$, corresponding to an approximately $57\%$ increase over the Hermitian value. Numerical results for three- and five-photon resonances closely reproduce the analytical transition times and yield non-negligible postselection probabilities. By contrast, the complete unconditioned dissipative evolution does not exhibit the same population-transfer enhancement. These results demonstrate a speed--success trade-off for measurement-conditioned multiphoton state transfer.

quant-ph↗

arXiv2026

Equivariant localization for higher derivative supergravity

Conformal supergravity provides an effective off-shell formalism to study higher derivative actions. We show that the $D=4$, $\mathcal{N}=2$ theory admits equivariantly closed forms. These may be used to compute closed-form expressions for supersymmetric observables in a general class of supergravity theories with higher derivative couplings, without any need to solve equations of motion. We discuss applications to holography, presenting results for on-shell actions that are conjecturally valid to all orders in the perturbative $1/N$ expansion.

hep-th↗

arXiv2025

One- and multiphoton resonances in the light-atom interaction

The interaction between atomic systems and electromagnetic fields is central to modern physics and emerging quantum technologies. The Rabi models, in their semiclassical and quantum versions, provide the simplest and most fundamental description of this interaction. In this work, we present a concise derivation of both models and show how one- and multiphoton resonances arise in the semiclassical regime. We then analyze how these resonances manifest in the quantum Rabi model, discussing similarities and differences in relation to the classical description. Special attention is given to the three-photon resonance, a phenomenon usually neglected in textbooks due to its relative weakness, but which is intrinsic to the radiation-matter interaction. Our goal is to offer an accessible pedagogical reference for students and researchers interested in Quantum Optics and Quantum Information, with an emphasis on the fundamentals of the Rabi models.

quant-ph↗

arXiv2025

Quantum Rabi oscillations in the semiclassical limit: backreaction on the cavity field and entanglement

The goal of this chapter is to compare the predictions of the semiclassical Rabi model (SRM), which describes the interaction between a two-level system (qubit) and a classical monochromatic wave, and the quantum Rabi model (QRM), under the assumption that the cavity field is initiated in a coherent state with a large average number of photons, ranging from 5K to 40K. First, we show that for a strong atom-field coupling, when the duration of the $\pi $-pulse (the time interval required to completely excite or deexcite the qubit in the resonant regime) is below $100\omega ^{-1}$, the behaviour of the atomic excitation probability deviates significantly from the textbook sinusoidal formula derived for the SRM under the rotating-wave approximation, and we present simple analytical and semi-analytical methods to describe more accurately the dynamics. Then we show that the QRM reproduces the qubit's dynamics predicted by the SRM only for initial times, since in the QRM the qubit excitation probability exhibits a collapse behaviour even in the lossless scenario; we also notice that the qualitative behaviour of such collapses is different from the ones occurring in the dissipative SRM. In the rest of this work we study numerically the backreaction of the qubit on the cavity field and the resulting atom--field entanglement, which are disregarded in the SRM. It is shown that the atom-field entanglement increases over time and a maximally entangled state is attained for large times. Moreover, we illustrate how the Rabi oscillations continuously modify the quantum state of the cavity field, which becomes increasingly different from the original coherent state as the time increases.

quant-ph↗

arXiv2024

Curvature effects on the regimes of the lateral van der Waals force

Recently, it has been shown that, under the action of the lateral van der Waals (vdW) force due to a perfectly conducting corrugated plane, a neutral anisotropic polarizable particle in vacuum can be attracted not only to the nearest corrugation peak but also to a valley or an intermediate point between a peak and a valley, with such behaviors called the peak, valley, and intermediate regimes, respectively. In the present paper, we calculate the vdW interaction between a polarizable particle and a grounded conducting corrugated cylinder, and investigate how the effects of the curvature of the cylinder affect the occurrence of the mentioned regimes.

quant-ph↗